Printer manufacturers want you to buy their ink and would like you to believe that knock-off ink is killing your printer. So is knock-off ink actually a bad idea? Yes and no.

StackExchange user cabbey explains that cheap printer ink is fine for regular-purpose printing, but if you need any real color accuracy you want to go with the official stuff:

There are all kinds of arguments around the quality, the longevity, potential damage to your print head, etc. But those are kinda irrelevant for "us" here on photo-SE.

If you're printing pretty office charts and graphics, SURE. That's what most of those inks are built for... some even brag about a "more vibrant red" with their ink.

If you're printing pictures, on decent paper that comes with ICC profiles...nope.

The problem is that all the profiles are built based on the original ink, you change to a different ink and the profiles are all wrong.

Now if you're printing ENOUGH volume, and you can find an ink vendor that's consistent, you could in theory pay to have your own profiles built for your printer, your paper and their ink. But you'll probably end up paying just as much for the custom profiles as you saved on the ink.

Basically, if perfect color is important you need to buy the good stuff. If not, knock-off brand ink shouldn't damage your printer.